Liquid polymer hydration

ABSTRACT

Described is a mixing apparatus and its use in the hydration of liquid polymers. The apparatus includes two packed mixing columns, each having two reducing couplings attached thereto to form an inlet and an outlet to each column. The outlet of the first mixing column is connected to the inlet of the second mixing column via means of a reducing passageway. The apparatus also has sources of supply for liquid polymer and water connected to the inlet of the first mixing column through metering means and injection check means. The apparatus provides controlled mixing velocity during the hydration with non-shearing agitation and without a chemical buildup.

This is a division of application Ser. No. 961,310, filed Nov. 16, 1978,now U.S. Pat. No. 4,201,867.

BACKGROUND OF THE INVENTION

A. Field of the Invention

This invention relates to the hydration of liquid polymers and, moreparticularly, to a novel apparatus and its use in the hydration ofliquid polymers.

B. Description of the Prior Art

Liquid polymers are increasingly used as flocculating agents in manywater and waste treatment installations. For example, liquid polymersmay be used in water treatments such as raw water clarification,municipal and industrial waste water clarification, chemical processwater purification and emulsion breaking.

For such uses, it is usually necessary that the commercially-available,concentrated liquid polymer solutions and dispersions be first hydratedto form a dilute aqueous solution having less than about 1.09% by weightliquid polymer present. However, much care is normally necessary forsuch hydration. In particular, the mixing time and relative amounts isusually closely controlled to avoid the formation of a water-insolublegelatinous mass of polymer which can lead to a waste of chemical andclogged process lines. Furthermore, the velocity during hydration isalso normally controlled so as to not cause agitation that may shearapart the polymer chains and thereby reduce the effectiveness of thepolymer.

In general, proposed prior art methods of hydrating liquid polymersinclude "in-line" mixers which make use of helix configurations inside asection of pipe. See, for example, Kenics Corporation sales brochureentitled "STATIC MIXER MODULES--DESIGN BULLETIN" effective Mar. 1, 1974;Kenics Corporation technical report entitled "OPERATION OF STATIC MIXERUNITS", 1976; and Komax Systems, Inc., sales brochure entitled "PROCESSCONTROL MOTIONLESS MIXING" Bulletin 103, effective September, 1976.However, such designs may not provide the close control of polymerhydration that is needed to prevent the problems of insoluble massformation and polymer shearing. Batch-type mixers have also beenproposed for hydrating liquid polymers. However, such apparatus requireslarge tanks and careful addition of the polymer to the water in order toprevent the formation of insoluble gelatinous masses.

BRIEF SUMMARY OF THE INVENTION

The present invention, therefore, is directed toward an apparatus and amethod for hydrating liquid polymers. The apparatus includes two packedmixing columns, each having two reducing couplings attached thereto toform an inlet and outlet to each column. The outlet of the first mixingcolumn is connected to the inlet of the second mixing column via meansof a reducing passageway. The apparatus also has sources of supply forliquid polymer and water connected to the inlet of the first mixingcolumn through metering means and injection check means.

The present method for hydrating liquid polymers includes feeding theliquid polymer and water into the above-defined apparatus in awater:polymer weight ratio of at least about 100:1; controlling thevelocity of the resulting mixture within the mixing apparatus andproviding a sufficient residence time of the mixture within theapparatus so that a homogeneous mixture free of insoluble masses iswithdrawn from the apparatus.

BRIEF DESCRIPTION OF THE DRAWING

The FIGURE illustrates a preferred embodiment of the present invention.

DETAILED DESCRIPTION

Referring to the FIGURE, the packed mixing columns 2 and 4 arepreferably made of oxidizing agent-inert plastic material and have walls6 which define confined spaces 8 and 10, respectively, for fluid flow inan overall mean flow direction approximately parallel to the columnswalls. Among these plastic materials are the synthetic materials whichare inert to oxidizing agent attack and which may be solvent welded.Particularly useful are the high polymer resins and plastics such aspolyvinyl chloride (PVC) and the like. However, the choice of materialis not critical to the present invention and it is well within theknowledge of one of ordinary skill in the art to select a suitablematerial which is commercially available.

The walls 6 of the mixing columns may be of any geometry desired as longas no pockets or corners are created in the direction of overall flow offluid in the columns which may creat detrimental chemical buildup. Forexample, the walls 6 may have a rectangular cross-section or a circularcross-section or any other configuration subject to the precedingproviso. A particularly advantageous geometry for these walls is asimple circularly cross-section, i.e., the walls are tubular.

An important aspect of the geometry of the mixing columns 2 and 4involves the avoidance of problematic pockets and increased mixingcapabilities by employing reducing couplings 12, 14, 16, and 18 at eachend of the two mixing columns to form an inlet 20 and an outlet 22 formixing column 2 and inlet 24 and outlet 26 for mixing column 4. Thesefour couplings may also be made of plastic materials such as polyvinylchloride (PVC) and may be advantageously solvent welded to the columnwalls. By solvent welding, the need for flanges and bolts is eliminatedand the likelihood of leakage during use is thereby substantiallyreduced. Additionally, couplings 12, 14, 16, and 18 have inwardlytapering surfaces 28, 30, 32, and 34, respectively, which reduced thecross sectional area of the confined spaces 8 and 10. Surfaces 28, 30,32, and 34 form angles of at least 110°, and preferably at least 125°,with wall 6 as shown by the dotted lines in the FIGURE. The formation ofangles this size, or greater, between the column wall 6 and the reducingsurfaces 28, 30, 32, and 34 assures that no pocket areas are creatednear the inlets 20 and 24 and the outlets 22 and 26 of the two mixingcolumns, respectively.

The outlet 22 of mixing column 2 is connected to inlet 24 of mixingcolumn 4 by means of a reducing passageway number 36. This reducingpassageway 36 provides a rapid velocity change for the aqueous solutionto enhance mixing. The length of this reducing passageway is notcritical to the present invention. However, it should be of sufficientlength to provide a cross-over manifold between the two mixing columns.The ratio of the average cross-sectional areas of the mixing columns,i.e., between walls 6, to that of the reducing passage should be about4:1 to about 20:1, preferably about 6:1 to about 15:1. The reducingpassageway, like the mixing columns, may be constructed of any suitablematerial, preferably PVC. The reducing passageway 36 may be attached tothe reducing couplings 14 and 16 by any desired means, includingthreaded joints or by solvent welding.

Mixing columns 2 and 4 contain packing material (not shown in theFIGURE) to increase the mixing of the liquid polymer and water in thecolumns. The preferred types of the packing material include ceramicsaddles and rings. However, it should be noted that it would be withinthe ordinary skill of one in this art to determine optimum type and sizeof packing material for each operation. Accordingly, the presentinvention is not intended to be limited to any particular type or sizeof packing material.

In the apparatus of the present invention, the inlet 20 of the firstmixing column 2 is connected to sources of liquid polymer and water viaseparate metering means and check valve. The usual source of the liquidpolymer is commercial drums or bulk storage tanks filled with thedesired polymer. The usual source of water is either the plant ormunicipal water supply. Preferably, it is desirable to employ freshwater rather than waste or process water. The metering means may be anyconventional structure or deisgn for motivating each starting materialat predetermined amounts or rates of flow from its source to the inletof the first mixing column. In the case of the liquid polymer, thepreferred metering means is a positive displacement pump. A simplerotameter is preferred for metering water. However, the metering meansmay instead by any other conventional gas, electric or gravity type flowregulated pumping system. The check valves serve to prevent back flow ofthe two starting materials into the feed lines. Preferably, anyconventional injection check valve can be employed for the liquidpolymer. Ball-type check valves are preferred for the water.

Thus, by reference to the FIGURE, liquid polymer source 38 is connectedto metering means 42 which is connected to injection check valve 44, thelatter being in turn connected through mixing tee 58 to the inlet 20 ofthe first mixing column 2; and water source 40 is connected to meteringmeans 46 which is connected to injection check valve 48, which in turnis also connected through mixing tee 58 to inlet 20.

In a preferred embodiment, additional water source 50 is connected at orafter outlet 26 of second mixing column 4 via conventional meteringmeans 52, check valve 54, and mixing tee 60. This additional watersource is preferably used to further dilute the hydrated liquid polymerto optimum concentration. Line 56 which is connected to outlet 26, takesthe hydrated liquid polymer to the desired water or waste treatmentfacilities.

Preferably, the described apparatus of the prevent invention may be mademodular in design to permit packaging for shipment. Accordingly, theentire apparatus can be bolted together on a metal or plastic mountingplate. The mounted assembly may then be in turn mounted on a plant wallor may be mounted on one or more posts or poles.

The apparatus of the present invention advantageously providescontrolled velocity during hydration with concurrent non-shearing mixingin a geometric configuration that prevents chemical buildup duringoperation. Moreover, other advantages of the apparatus of this inventioninclude a system that has no moving parts and the easy feeding of liquidpolymer directly from a drum or bulk storage tank into the first mixingtank.

In an embodiment of the method of the present invention, the first stepis having a liquid polymer and water separately fed from their sourcesto the inlet of a first packed mixing column via individual meteringmeans and check valves. The weight ratio of water to liquid polymerbeing fed is greater than about 100:1, preferably in the range of about150:1 to about 400:1.

Typical liquid polymers for the present invention includepolyacrylamides, cationic-modified polyacrylamides, anionic-modifiedpolyacrylamides, polyacrylates and polyquaternaryamides that areconventionally used in water treatment. These polymers usually arecharacterized as having a relatively high viscosity (e.g., from about250 to greater than about 5,000 centipoise at 25° C.) and relativelyhigh molecular weights (e.g., in the 200,000 to over 10 million range).Such unhydrated liquid polymers are commercially available inconcentrated aqueous solutions or concentrated aqueous dispersions(i.e., concentrated aqueous solutions of liquid polymers also containinga hydrocarbon carrier such as xylene or the like). For purposes of thisinvention, an unhydrated liquid polymer that is to be hydrated accordingto the present invention is defined to mean polymer solutions assupplied commercially in neat or undilute form.

The next steps of the present invention are sequentially passing themixture of liquid polymer and water through the first packed mixingcolumn, then through the reducing passageway and through the secondpacked mixing column and finally withdrawing the hydrated polymer fromthe outlet of the second packed mixing column for later application atthe desired water treatment facilities. It is important that thevelocity of the mixture be controlled during the passage through thecolumns and reducing passgeway, otherwise, possible undesired shearingof the polymer may occur. Accordingly, it is desirable that velocity ofthe mixture in the two packed mixing columns be less than about 1.0 footper second, more preferably, less than about 0.5 foot per second, andthe velocity in the reducing passageway be less than about 7.0 feet persecond, more preferably, less than about 3.5 feet per second.Furthermore, the retention time within this three-stage mixer should besufficient to effect a homogeneous hydrated mixture free of insolublemasses. Usually, an overall retention time of about 30 seconds to about300 seconds, more preferably, from about 60-120 seconds, is desirable toachieve this result.

After withdrawing the hydrated polymer from the mixing apparatus, it maybe directly transferred to the desired water or waste treatmentoperation for use as a flocculating agent or the like.

In a preferred embodiment of the present method, the hydrated polymermay be further diluted with additional water so as to achieve theoptimum concentration of polymer in the water for best flocculatingresults. Accordingly, it may be desirable, depending on the liquidpolymer and the intended use, to dilute the hydrated polymer exiting theoutlet of the second packed mixing column with from about 1 to about 10times more water, more preferably, from about 2 to about 5 times morewater.

The following example further illustrates the present invention. Allparts and percentages are by weight unless otherwise indicated.

SPECIFIC EXAMPLE

The novel apparatus shown in the FIGURE was used as follows.

A large U.S. Southern petrochemical company required the use of a liquidpolymer flocculating agent in a waste water treatment clarifier tosettle suspensed solids. An anionic polyacrylamide-type of polymer in awater-oil emulsion was selected for this use.

This polymer was fed into the apparatus illustrated by the FIGURE at arate of about 25 to 30 gallons per day on a continuous feed basis via apositive displacement metering pump and a ball-type injection checkvalue to the inlet mixing tee. Plant water was simultaneously fed tothis mixing tee via a conventional 1/2-inch rotameter and check valve atthe rate of about 3.5 to about 4.2 gallons per minute, also oncontinuous feed basis.

This mixture, after said mixing tee, passed vertically through a firstpacked mixing column of 4 inch diameter and 48 inch height, constructedof PVC and provided with inlet and outlet reducing couplings havinganlges of at least 125° with the column walls as shown in the FIGURE.The mixing column was packed with 0.32 cubic feet of 1 inch Burlsaddles.

After passing through this packed column, the liquid mixture passedthrough a reduced passageway of 0.75 inch nominal pipe size and about 18inches of length. This passageway was also composed of PVC. The velocityof mixture through this reduced passageway was calculated to be about2.1-2.5 feet per second.

Next, the mixture was passed through a second packing mixing column ofthe same geometry as the first column. This second column was alsopacked with 0.32 cubic feet of 1 inch Burl saddles. After a 60 secondretention time, the hydrated liquid polymer exited the second mixingcolumn in a homogeneous condition and free of insoluble masses. Afurther H₂ O dilution was provided through 3/4-inch rotameter at a rateof 5 gallons per minute as indicated in the FIGURE, to further dispersethe hydrated liquid polymer. This second dilution further increased theweight ratio of H₂ O to liquid polymer by a factor of at least 2:1. Thishydrated liquid polymer performed satisfactorily for the purpose it wasintended.

What is claimed is:
 1. An apparatus for the hydration of liquid polymers comprising:(a) first and second packed mixing columns, said columns made of oxidizing agent-inert plastic material, and said columns having walls defining a confined space for fluid flow in an overall mean flow direction approximately parallel to said walls; (b) two reducing couplings for each of said columns, one of said couplings being located at one end of said column and attached to said walls to form an inlet and the other of said couplings being located at the other end of said column and attached to said walls of said column to form an outlet, said couplings having surfaces which reduce the cross-sectional area of said confined space defined by said column walls, said coupling surfaces forming an angle of at least 110° with said column walls; (c) said outlet of said first mixing column connected to said inlet of said second mixing column by means of a reducing passageway; the ratio of the average cross-sectional areas between said confined spaces defined by said column walls and said confined space defined by the reducing passageway walls is from about 4:1 to about 20:1, (d) a first check valve connected to said inlet of said first mixing column; (e) a liquid polymer source; (f) a metering means connecting said first check valve to liquid polymer source; (g) a second check valve connected to said inlet of said first mixing column; (h) a water source; and (i) a second metering means connecting said second check valve with said water source.
 2. The apparatus of claim 1 wherein a second water source is connected to said outlet of said second packed mixing column.
 3. The apparatus of claim 1 wherein said first and second packed mixing columns, said reducing couplings and said reducing passageway are all composed of polyvinyl chloride.
 4. The apparatus of claim 1 wherein the packing for said first and second mixing columns is saddles. 